Reports on abundance and biological information of toothfish in Division 58.4.3b by Shinsei Maru No.3 in the 2010/11 and proposal of the consecutive survey in the 2011/12

In accordance with the Conservation Measure 41-07 (2010), a survey was conducted in order to collect information for the stock status and biology of toothfish in the southeast sector (24 allocated hauls) of Division 58.4.3b (BANZARE Bank), using a commercial bottom longline vessel Shinsei Maru No. 3, from May 7 to 16, 2011. Shinsei Maru Trot line system was used as fishing gear for 19 hauls. Comparison test using trotline and Spanish line systems were made for 5 hauls. Total catch (excluding fish released alive) of Dissostichus spp. and other bycatch species was 12.0 tonnes in the SE sector, where the catch limit of 15 tonnes was set. Dissostichus spp. made up 90.3 % in terms of weight of the whole fish caught. CPUE of Dissostichus spp. was 105.9 ± 16.2 kg / 1,000 hooks (mean ± SE) for the hauls where trotline system was employed. This was lower than 125 ± 13.1kg / 1,000 hooks in the 2009/10 survey, although there was no significant difference. Among two species of toothfish, Dissostichus mawsoni was dominant (79 % in weight to the total toothfish). D. mawsoni was mainly caught at 1300-1700 m depths while D. eleginoides at 700-900 m depths. Both maturity index and relative weight of gonads to body weight for D. mawsoni. were higher than those recorded in the previous two fishery periods conducted in earlier seasons (December-February in 2008/09 and 2009/10). However, those indices for D. eleginoides did not varied among the three years. Total of 62 individuals of toothfish with good physical condition were tagged and released during the survey. No toothfish was recaptured. The overlap of size between the fish released with tag and that of overall catch was considerably high (85 % for D. mawsoni and 79 % for D. eleginoides).

We propose to continue the survey focusing the mark recapture experiment for the next 2011/12 survey with the same designs as in the 2010/11.